Marijuana is the most frequently used illicit drug in the United States, especially among youth. Marijuana use has been linked to positive and negative affect, but to date research designs have not permitted a true test of an affect regulation model of marijuana use. Furthermore, studies have not adequately distinguished dispositional (trait) negative affectivity from state negative affectivity (e.g., depression or anxiety) from momentary negative affect as predictors of use. This study proposes using innovative methods (1) to examine the feasibility of recruiting 15- to 24-year old medical clinic patients with current, frequent use of marijuana to a two-week momentary sampling study, (2) to test an affect regulation model for marijuana use among youth who are frequent marijuana users, and (3) to determine the contributions of trait negative affectivity and state negative affect (depression and anxiety) to marijuana desire/use and the associations between marijuana use and subsequent affect. Taking advantage of the unique data collected with momentary sampling, analyses will also explore the effects of social context, such as companionship and location, on marijuana desire and use. Seventy-six patients 15 to 24 years of age who report marijuana use at least twice a week will be recruited from an adolescent/young adult medical clinic to achieve a sample of 60 youth who complete the protocol. Audio computer-assisted self-interview (A-CASI) will be used to assess demographic and personality characteristics, depression and anxiety, marijuana use diagnoses, and other substance use, and a timeline follow-back (TLFB) calendar will be used to recall marijuana use events over the previous two weeks. Participants then use a handheld computer for two weeks, responding to random signals (~70 signals each, up to 4,200 signals total) with reports of their affect, social context, desire to use, and use of marijuana as well as other drugs. Participants also will also initiate a report at the onset of and after marijuana use events. At the end of the two weeks, participants will recall average affect by A-CASI and specific affective states and marijuana use by TLFB calendar for the same period. Data will be analyzed using cubic spline regression models. Establishing the feasibility of momentary sampling methods to study affect regulation among young marijuana users will be essential to further testing affect regulation models of marijuana use and ultimately developing affective-sensitive interventions for this high-risk population. The epidemic of marijuana use disorders among adolescents and young adults mandates research to improve our knowledge of how use and abuse are initiated and sustained in this population and to use this knowledge to develop novel approaches to prevention and treatment. We hope that findings from the proposed research will significantly advance our understanding of how youth may use marijuana to regulate their feelings and therefore may have important implications for prevention. [unreadable] [unreadable] [unreadable]